Near-field communication (NFC) is a short-range wireless communication technology that is used for exchanging data between devices over short distances of up to a few tens of centimeters.
NFC is used in many types of so-called contactless devices, such as travel cards, credit cards and the like. In addition, NFC can be used in radio-frequency identification (RFID) applications whereby a reader device can detect and retrieve data from an NFC tag. RFID devices comprise an antenna, which is used for the transmission and reception of radio signals (data), and as an induction loop for powering the device, whereby the NFC tag is able to be powered by an RF induced current in its antenna as it resides within the RF field of the reader device.
NFC devices communicate via magnetic field induction whereby the loop antenna of the reader device and the loop antenna of the NFC device are located within each other's near field, effectively forming an air-core transformer. By such a configuration, it is possible to transmit data and power from one device to the other.
There are generally two modes of NFC: a passive communication mode whereby the initiating device provides a carrier field and the target device answers by modulating the carrier field; and an active communication mode where both the initiating and target devices communicate by alternately generating their own fields.
The target device can be a smartcard or a tag, but also more advanced devices, such as mobile phones can have NFC functionality whereby they “emulate” the behavior of an NFC tag. For this reason, when the target device operates in passive communication mode, this is usually called a “tag emulation mode” and the target device can be called a “tag emulator” or “transponder”. Such devices can communicate with one another according to operations and protocols defined by the ISO 14443 standard. A problem can arise, however, where more than one NFC reader and/or target are in range of one another, because this can lead to data collision and unnecessary bandwidth being used.
Specifically, certain types of passive NFC tags can cause coexistence problems in NFC environments. Specifically, one type of NFC tag, which is an RF barcode-type device developed and marketed by the company Kovio™, (commonly referred to as a “Kovio tag”), comprises a printed integrated circuit (PIC) comprising an antenna, a master circuit, a transponder and a 128-bit ROM.
The ROM is loaded with a unique identification code (UID), and the device operates in a passive, read-only mode.
As such, when the RF barcode device enters the RF field of a reader device, it is powered-up and by an induction current in its antenna, and then proceeds to broadcast its 128-bit code (the UID) at intervals. In other words, the RF barcode device operates in a Tags-Talk-First (TTF) mode, it does not accept any commands from a reader but rather, as soon as it receives enough power from the reader's field to operate, it repeatedly transmits its UID at a specific interval, as long as it is powered.
Specifically, an RF barcode device is configured to begin broadcasting its UID within 1 ms of entering the RF field (or the RF field being switched on). It takes approximately 1.21 ms to broadcast the 128-bit UID, assuming a bit rate of 106 kbps, and this process is repeated every 3.6 ms (the “sleep duration”) as long as the RF field is present, as depicted in FIGS. 1 and 2 of the drawings.
In FIG. 1, which shows the RF field 10 and the RF barcode device response 12 as a function of time on the horizontal axis, it can be seen that the RF field is initially OFF, but after time t1, it is switched on. The RF barcode device is powered-up and activated by the RF field, and within 1 ms of t1, begins broadcasting its UID 14.
As can be seen from FIG. 2 more clearly, the UID 14 is made up of a number of pulses representative of the UID. Each bit 16 takes 9.44 μs to transmit, so a 128-bit UID takes 1.21 ms to transmit, assuming a bit rate of 106 kbps. The sleep interval 18, i.e. the wait time between successive UID transmissions 14, is 3.6 ms.
On the other hand, NFC-A tags (or other listen mode devices) work in a Request-Response mode, and therefore wait for an NFC-A Poll Request from an NFC reader device before transmitting the NFC-A Poll Response.
For the avoidance of doubt, NFC Forum “Type-1 Tag” (T1T), “Type-2 Tag” (T2T) and “Type-4A Tag” (T4AT) are all based on NFC-A technology. As such, the terms “NFC-A tag” and “NFC-A listen mode devices” are essentially the same. NFC-DEP based peer-to-peer (P2P) target devices may also be based on NFC-A technology.
As such, until the RF barcode device leaves the RF field, it will continue to broadcast its UID. Moreover, because the RF barcode device cannot accept a power-down command from the reader device, to halt, or pause, the RF barcode device's UID transmission, other NFC traffic, for example, between the reader and other NFC-A devices is adversely affected.
At present, there are no guidelines for reading RF barcode-type devices alongside other NFC-A devices (in reader mode or card emulation mode) and the fact that the RF barcode device, by design, repeatedly broadcasts its UID, can cause data collisions or adversely affect the stability of the reader device, which degrades the user experience.
The reason for this is that the Kovio standard specification, as shown in FIG. 3, imposes a guard time of 5 ms for polling the NFC-A tags. This means that when the RF field is switched on, the RF barcode devices activate within 1 ms, whereas other NFC-A devices are not polled until 5 ms after switching on the RF field. The problem is that when an RF barcode type device (e.g. a “Kovio tag”) is detected by an NFC reader, the NFC reader cannot poll for NFC-A tags. As a result, the NFC reader will switch OFF the RF field upon detection of only RF barcode devices, resulting in a bad user experience because the NFC reader won't detect any NFC-A tags even though NFC-A tags may be present in the RF field.
Referring to FIG. 3, the sequence commences by switching ON 20 the RF field, whereupon the ISO 14443-3 polling loop protocol is initialized 22. Within 1 ms, 24, polling begins, which starts a “seek” procedure 26. During the seek procedure 26, a guard time 28 of 5 ms 28 is waited-out. If an RF barcode device is present in the RF field, i.e. if the NFC reader receives the 1st bit 30 before the expiry of the 5 ms guard time 28, then the RF barcode device is deemed “detected” 32 and the remainder of the UID is obtained 34.
On the other hand, if 5 ms guard time 28 expires without detecting an RF barcode device, then the NFC reader will proceed to poll for NFC-A devices in the usual way 36.
As can be seen from FIG. 3, the NFC reader will proceed to poll for NFC-A tags 36 only if it does not detect an RF barcode device within 5 ms 28 of switching ON the RF field.
A need therefore exists for a solution that makes it possible for RF barcode-type devices to coexist with other types of NFC devices in an NFC environment, for example, enabling RF barcode devices and other ISO 14443-compliant devices to cohabit and interoperate in parallel with a common reader device.